The present invention relates to a modified medium-or low-density polyethylene composition.
The linear medium- or low-density polyethylene produced by the copolymerization of ethylene with other .alpha.-olefins exhibits excellent tensile strength, impact strength, rigidity, environmental stress cracking resistance (hereinafter referred to "ESCR") and thermal resistance as compared with the highly branched low-density polyethylene produced by the high pressure radical polymerization of ethylene. Accordingly, films or various molded articles obtained by injection molding, blow molding, extrusion molding or rotational molding of this linear medium- or low-density polyethylene exhibit properties, even at a thinner section thickness or at a lighter weight, comparable to those obtained from highly branched low-density polyethylene and, therefore, the linear medium- or low-density polyethylene is industrially valuable from the viewpoint of conserving raw materials and energy. Further, the linear medium- or low-density polyethylene has the above described excellent various properties, and accordingly can be employed under more severe conditions than a highly branched low-density polyethylene and can be made into articles having a high functionality.
Such a linear medium- or low-density polyethylene, however, has the following disadvantages compared with a highly branched low-density polyethylene. Namely, the transparency is inferior and accordingly, from the viewpoint of the external appearance of articles the commercial value is inferior. Also the melt tension and the melt elasticity are low and as a result, it is difficult to produce various molded articles by blow molding, extrusion molding and film molding and thus the molding conditions must be disadvantageously controlled in a narrow range. Moreover, in order to overcome these defects, the molding machines must be improved in a specific way and this is economically unfavorable.